基于F-J-M法的桥梁温度与地震作用效应组合研究

Study on Combined Effects of Bridge Temperature and Seismic Actions Based on F-J-M Method

目前铁路桥梁设计逐渐由容许应力法向极限状态法转变,而《铁路桥涵设计规范(极限状态法)》(Q/CR 9300—2018)并未提及地震作用与温度等可变作用的联合作用,给高寒高烈度区桥梁结构抗震设计带来了较大困难。为了推进桥梁以更经济的抗力方式抵御外荷载作用,通过目标可靠度指标确定其最优地震设计状况荷载组合分项系数,从而对现行桥梁设计规范抗震设计进行优化。建立了高寒地区某桥温度作用效应概率模型,使用Ferry Borges荷载组合理论探究地震和环境温度作用的效应分布特征,并基于JC法和多灾害荷载系数设计法(MH-LRFD)建立地震、温度作用荷载系数的表达式。依托某桥梁工程实例分别探究了地震、温度以及两者共同作用下的桥梁的失效概率。研究结果表明:环境温度引起的桥梁温度内力响应、主要构件材料特性变异均能显著影响桥梁的失效概率;对于高寒大温差地区,现行规范忽略环境温度效应将显著低估桥梁在地震作用下的失效概率。本文提出的F-J-M(Ferry Borges+JC+MH-LRFD)方法计算地震、温度作用组合系数,可为高寒地区桥梁抗震设计提供必要理论依据。

Currently,the design of railway bridges is gradually transitioning from the allowable stress method to the limit state method.However,the Code for Design on Railway Bridge and Culvert(Limit State Method)(Q/CR 9300-2018)does not account for the combined effects of seismic actions and variable factors such as temperature,posing significant challenges for seismic design for bridges in areas of extreme cold and high seismic intensity.In order to promote bridge resistance to external loads in a more cost-effective way,the partial coefficient of the optimal seismic design condition load combination was determined by target reliability indices,thereby optimizing the seismic design stan-dards in current bridge design codes.A probability model for temperature effects on a bridge in cold re-gions was established.The distribution characteristics of the effects of earthquake and ambient temper-ature were explored using the Ferry Borges load combination theory.Expressions of the load factor of earthquake and temperature effects were established using JC method and multi-hazard load factor de-sign method(MH-LRFD).Taking a practical bridge engineering project as an example,the failure probabilities of a bridge under earthquake,temperature,and their combined actions were explored re-spectively.The results showed that both the temperature internal force response caused by ambient temperature and the variation in properties of the bridge′s main components significantly affected its failure probability.For extreme cold regions with significant temperature variations,ignoring ambient temperature in the current codes would significantly underestimate the failure probability under seismic actions.The proposed F-J-M(Ferry Borges-JC-MH-LRFD)method can be used to calculate the com-bined coefficients for earthquake and temperature actions,providing a necessary theoretical basis for the seismic design of bridges in extreme cold regions.